Year-Round Food Production: So Much More Than a Greenhouse

| 11/21/2014 9:31:00 AM

Tags: greenhouse, food, Colorado, David R. Braden IV,

For anyone eating on a budget, or living in a food desert where it is difficult to get to the grocery store, protein and fresh vegetables become luxuries. Without protein and fresh vegetables human health is compromised. Access is particularly limited where fresh vegetables cannot be grown outdoors during the winter. Carbohydrates like beans, rice, potatoes and pastas come cheap in bulk and store easily but animal protein and vegetables are best eaten fresh. A greenhouse is an option for winter vegetables but any savings can be lost if you have to heat the greenhouse.

We are developing ways to address these issues by designing for a relatively inexpensive structure that can be attached to the south side of a building to produce protein and fresh vegetables year round. To avoid the expense of gas or electric heat we are enclosing enough thermal mass to absorb extra heat when the sun is shining and release it when the sun goes down. The formula from the passive-solar greenhouse literature is that we need between 2 and 5 gallons of water, or equivalent, (masonry gives you about ¼ of the heat storage as the same volume of water) for every square foot of glazing. It also turns out that the type of glazing is less important than how well we are able to seal the structure against air leaks. We also get credit if the wall to which we attach the structure is heated from the other side.

We are not purists so we do not mind adding “active” elements to the system and we like to have each element serve multiple purposes. We like to try things and see how they work. Also, this structure is a part of our wider explorations into how we can work with nature and use natural processes to reduce our work load.

Integrated Closed Loop Production Systems

Nature works in cycles that have no cost and produce no waste. That is what makes natural systems sustainable. To reduce our cost of inputs to zero we have to close the loops and produce all of our inputs as a part of the production cycle. To reduce our waste to zero we have to integrate the processes and find a use for all the byproducts of each process. Those parts of the cycle that cannot survive freezing can be enclosed in a shell designed to retain the sun's heat during the day and release it at night.

Our first prototype is attached to the south wall of an occupied residential dwelling. We used two layers of greenhouse film over 2-by-4 framing. The north wall of our structure is constantly 65 to 70 degrees Fahrenheit and we have no heat loss in that direction. We built raised beds 3 feet wide and 3 feet deep in order to increase the ratio of thermal mass to air space. In the raised beds we installed a pipe attached to a fan that takes air from the top of the structure and blows it through the growing medium to actively transfer heat into and out of the growing medium. The growing medium is wood chips and horse manure like our outside gardens. The fan runs all winter long pumping heat into the bed when the sun is shining and pumping heat out of the bed at night. This heat storage system is called a climate battery and is based on designs developed at the Central Rocky Mountain Research Institute in Basalt, Colorado.

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